An internal combustion engine comprises at least one cylinder, in which a piston, connected mechanically to a drive shaft, moves back and forth. The cylinder is connected to an intake manifold by at least one intake valve, and to an exhaust manifold by at least one exhaust valve. And the position of the intake and exhaust valves of a conventional internal combustion engine is controlled directly by one or two camshafts powered by the drive shaft.
A new type of internal combustion engine (known commercially as “Multi-Air”) has recently been proposed comprising a valve opening control device, which controls the opening angle and lift of the intake valves to control the power generated by the engine. The valve opening control device employs a conventional camshaft powered by the drive shaft, and comprises, for each intake valve, an electrically controlled hydraulic actuator (i.e. controlled by a solenoid valve) interposed between the intake valve stem and the camshaft. By controlling each hydraulic actuator, the power transmitted by the camshaft to the intake valve stem can be adjusted to adjust the actual lift of the intake valve. In other words, the control device adjusts the actual lift of the intake valve of each cylinder at each engine cycle, independently of the other intake valves.
In the event of a malfunction in the hydraulic circuit of the valve opening control device hydraulic actuators, or in a hydraulic actuator or solenoid valve of the control device, the position of one or more intake valves may not be controlled correctly (typically, the intake valve may not open). In other words, opening of the intake valves is not guaranteed mechanically by the camshaft, because of the hydraulic actuators between the camshaft and the intake valve stems. Which means that a malfunction in the hydraulic actuators or the control/power chain of the hydraulic actuators may prevent the intake valves from opening correctly.
Malfunctions of this sort never have a destructive effect on the internal combustion engine—on account of the maximum travel of the intake valve being determined by the camshaft profile, which is designed to prevent any mechanical interference between the intake valves and pistons—but must be diagnosed immediately, because of the negative effect they have on the power generated by the engine and the quality of combustion inside the cylinders.
To diagnose non-opening of one or more intake valves, it has been proposed to provide each intake valve with a position sensor (possibly an ON/OFF type, i.e. a microswitch) to real-time determine the actual position of the valve. This solution, however, involves considerable cost, not only in terms of purchase, installation and wiring, but also to insulate the position sensors to withstand the high temperatures generated in the cylinder head area of an internal combustion engine.
US2008236267A1 describes a method of determining correct opening of internal combustion engine intake and/or exhaust valves, by determining the intake pressure along an intake pipe of the engine; comparing the intake pressure with a reference signal; and diagnosing operating failure of the intake and/or exhaust valves when the difference between the intake pressure and the reference signal exceeds a given tolerance threshold.